Keyword frequency

I'm somewhat new to SEO and not clear about optimal use of keywords and phrases. Say I have a blog and I want to target the keyphrases "fried green tomatoes", "used farm equipment" and "outstanding okra recipes".

1. If I can publish three posts a week and can use three phrases in each post, which is better for elevating their ranks: a. Use the same phrase three times in one post a week, or b. Use all three phrases in each post?

2. All other things being equal, how many times do I need to publish a keyword or phrase to raise its ranking? To illustrate my question with a simple example: If there are ten sites with the same site and page ranks as mine publishing a keyphrase, can I outrank them by just using the phrase more often than they do?

I realize that there are lots of variables besides keywords that affect ranking but I am just trying to get some idea of how much I should use my target keywords before I move on to some new ones. Thanks!